In recent years, the airline boarding pass has gone from a bulky packet of paper you received in the mail to an e-mail that you can print out at home.

But the incredible shrinking boarding pass may not be done evolving. Soon, it may become a tiny digital bar code that sits on your cell phone screen.

So said a trade association for international airlines Thursday. The International Air Transport Association, which represents 240 airlines, said it has taken a step toward allowing passengers to check in for flights using a bar code sent to their cell phones via e-mail or text message, making the process truly paperless.

Passengers would simply show airport officials their phone screen and off they go. A version of the system is being tested by Air Canada, but it looks like it will be a few years before it is adopted in the United States.

Technically, what the airline trade group did Thursday was agree on a global standard for the bar code that would be used.

According to the association's plan, passengers would register their mobile phone, personal digital assistant or smart phone when buying a ticket. They would receive a text message with a bar code, or instructions to download it. The bar code would become the passenger's boarding pass and it would be read directly from the screen of the mobile device, said the association.

U.S. carriers were among those who signed off on the standard for the bar code, but implementation of the plan in this country will require authorization by authorities including the Transportation Security Administration, which requires passengers show a photo identification and boarding pass, noted Steve Lott, a spokesman for the International Air Transport Association in Washington.

The association members represent 94 percent of international air traffic, and they have been working on bar-coded boarding passes as part of a larger effort to make the industry more efficient, said Lott. He said the association believes the process will save more than $500 million annually when fully implemented.

"Passengers want the convenience of self-service options in a paperless environment," said Giovanni Bisignani, director general and chief executive of the International Air Transport Association in Geneva. "This standard (bar code approved by members) is an important step in getting rid of paper that bogs down processes and drives up costs."

He said that in the next few months the association staff and its members will focus on guidelines for global implementation.

Jeff Kovick, a spokesman for United Airlines in Chicago, said the carrier had agreed to the bar code standard and is considering the option.

Tim Wagner, a spokesman for American Airlines in Fort Worth, Texas, said the use of bar codes on cell phones that would serve as boarding passes "is something we will examine closely." He said no decision to use the technology has been made and there is no timeline for that decision.

In Houston, Mary Clark, a spokeswoman for Continental Airlines, said, "This kind of technology is very consistent with our initiative to be paperless." She added, "The plans for (going paperless) are not definitive and work needs to be done before it could be implemented. But for a traveler who is going to be flying with a digital handheld device anyway, eliminating the extra piece of paper can be a benefit."

Air Canada implemented paperless boarding passes for customers who check in using cell phones or devices such as a BlackBerry or Treo on Sept. 21. The carrier's mobile check-in service - mobile.aircanada.com- was enhanced to offer customers the option of receiving an electronic boarding pass in the form of text messages that the customer simply shows to airport security screening personnel and Air Canada gate agents.

The service is available for flights in Canada and departures to international (but non-U.S.) destinations.

Lott, the trade association spokesman, said other international carriers using the technology include ANA in Japan, Air Berlin in Germany and Spanair in Spain.